The present invention relates to radiation-curable, optical fiber coating compositions, which are adaptable for forming coatings such as inner primary coatings, outer primary coatings, colored secondary coatings, ink coatings, bundling materials, ribbon matrix materials and colored matrix materials on optical fibers. The compositions comprise acrylated acrylic oligomers. The present invention also relates to a coated optical fiber.
Radiation-curable compositions are vital to the optical fiber industry. Materials used in the manufacture of optical fibers are typically sensitive to environmental and handling stresses and can be made of glass, for example. Radiation-curable compositions have been formulated to provide protective coatings for sensitive optical fibers. Such compositions include, among others, inner primary coatings, outer primary coatings, colored outer primary coatings, single coatings, matrix materials, colored matrix materials, bundling materials, inks, adhesives, and upjacketting coatings. Optical fiber cable manufacturers increasingly demand better performance from these coating compositions in order to allow the optical fiber to function in a wider array of environments and have better transmission performance In addition, compositions are demanded which deliver high performance at reduced cost.
Optical fiber assemblies provide a modular design which simplifies the construction, installation and maintenance of optical fibers by eliminating the need to handle individual optical fibers. Examples of optical fiber assemblies include ribbon assemblies and cables. A typical optical fiber assembly is made of a plurality of coated optical fibers which are bonded together in a matrix material. Such optical fiber assemblies containing a plurality of coated optical fibers have been used for the purpose of multi-channel transmission. The matrix material can encase the optical fibers, or the matrix material can edge-bond the optical fibers together.
Coated optical fibers for use in optical fiber assemblies are usually coated with an outer colored layer, called an ink coating, or alternatively a colorant is added to the outer primary coating to facilitate identification of the individual coated optical fibers. Thus, the matrix material which binds the coated optical fibers together contacts the outer ink coating if present, or the colored outer primary coating.
When a single optical fiber of the assembly is to be fusion connected with another optical fiber or with a connector, an end part of the matrix layer can be removed to separate each of the optical fibers.
Desirably, the primary coatings on the coated optical fibers, and the ink coating if present, are removed simultaneously with the matrix material to provide bare portions on the surface of the optical fibers (hereinafter referred to as xe2x80x9cribbon strippingxe2x80x9d). In ribbon stripping, the matrix material, primary coatings, and ink coating, are desirably removed as a cohesive unit to provide a clean, bare optical fiber which is substantially free of residue.
The production of and useful characteristics for coated optical fibers are discussed in, for example, U.S. Pat. No. 5,104,433, which is hereby incorporated by reference. Single mode or multimode fiber can be prepared. Step index and graded index fibers can be prepared. In the coated fiber, loss due to absorption, scattering, macrobending and microbending should be minimized. Avoiding microbending loss is particularly important. Optical fiber typically is about 125 microns in diameter, and coating layers of approximately 30 microns are applied thereto.
Optical fiber ribbons are described in, for example, U.S. Pat. No. 4,900,126 to Jackson et al.; U.S. Pat. No. 5,373,578 to Parker et al., U.S. Pat. No. 5,379,363 to Bonicel et al.; the complete disclosures of which are hereby incorporated by reference. Ribbon stripping is discussed in, for example: xe2x80x9cTesting of 4- and 8-Fiber Ribbon Strippabilityxe2x80x9d, G. A. Mills, Int. Wire and Cable Symp. Proc., 1992, pgs. 472-474; xe2x80x9cThe Effect of Fiber Ribbon Component Materials on Mechanical and Environmental Performancexe2x80x9d, K. W. Jackson et al., Int. Wire and Cable Symp. Proc., 1993, pgs. 28-34; which are hereby incorporated by reference.
In addition to ribbon packaging, fiber designs can include tight buffer, loose tube, filled loose tube, and mini-bundle. Cables can be packaged by conventional buffering, stranding, and jacketing steps. Optical fiber fabrication is disclosed in, for example, the article xe2x80x9cFiber Opticsxe2x80x9d Encyclopedia of Chemical Technology, Vol. 10, 4th Ed., pg. 514-538, (John Wiley and Sons, 1993), which is hereby incorporated by reference.
Inner primary coatings, outer primary coatings and matrix materials are usually formed from radiation-curable systems. Ink coatings usually are formed from a pigment dispersed within a radiation-curable system. The UV curable systems contain a UV curable oligomer or monomer that is liquid before curing to facilitate application of the composition, and then a solid after being exposed to UV radiation.
Modern high speed optical fiber drawing towers and ribbon forming towers operate at a very high speed. Thus, the radiation-curable compositions for forming inner primary, outer primary and ink coatings must have a very fast cure speed to ensure complete cure of the coatings and matrix material. In addition, the compositions should not contain ingredients that can migrate to the surface of the optical fiber and cause corrosion. Such additives are xe2x80x9cfugitivexe2x80x9d or free to migrate from the cured coating. Fugitive additives are generally undesirable because they might, for example, migrate and attack the optical fiber or be incompatible and cause loss of optical clarity. The compositions should also not contain ingredients which can cause instability in the protective coatings or matrix material. Ink coatings for optical fibers should be color fast for decades. The coatings and matrix material should not cause attenuation of the signal transmission and be impervious to cabling gels and chemicals.
Each of the coatings on the optical fiber and matrix material should be resistant to degradation caused by heat or light which can result in discoloration or even loss of integrity of the coatings or matrix material. If coating integrity is lost, the optical fiber may not be adequately protected from the environment resulting in signal attenuation. If one of the coating layers discolors, misidentification of the individual optical fibers may occur during splicing. Thus, there is a need for a radiation-curable coating composition suitable for application as a coating on an optical fiber, such as an inner primary coating, outer primary coating, colored secondary coating, ink coating, bundling material, ribbon matrix material and colored matrix material that exhibits substantial resistance to degradation caused by heat or light.
Current optical fiber coatings and matrix materials utilize acrylate functional monomers and acrylate functional oligomers. The oligomer backbone is usually derived from one or more polyether, polycarbonate, polyester or hydrocarbon polyols bound together via urethane linkages, to which acrylate functional groups are bound via urethane linkages. Thus, the oligomers used are generally acrylated polyurethanes. Optical fiber coatings and matrix materials can degrade when exposed to heat, causing undesirable yellowing and even loss of integrity of the coating or matrix material. Thus, there is also a need for radiation-curable compositions which exhibit enhanced resistance to thermal degradation.
Urethane acrylate oligomers are most widely used in the industry. Organofunctional silane coupling agents (or xe2x80x9cadhesion promotersxe2x80x9d) are also commonly used in the inner primary coating. For outer primary coatings, colored outer primary coatings and matrix materials, important additives include slip additives which function to lower the coefficient of friction of the cured material. A low coefficient of friction is important for processing and handling of coated optical fiber or optical fiber ribbon.
Typical urethane acrylate containing compositions have, upon cure, relatively high coefficients of friction. Therefore, despite problems associated with use of fugitive additives, slip additives are generally required in many cases to achieve the necessary performance. Hence, a need exists to lower the coefficient of friction of cured urethane acrylate compositions without the use of slip additives, and in particular, without fugitive slip additives.
From the above, it is clear that optical fiber technology places many unique demands on radiation-curable compositions which more conventional applications, such as printing inks and paints, do not.
Formulation and application of radiation-curable compositions for fiber optic materials in general and optical fiber coatings in particular can be found in, for example, U.S. Pat. Nos. 4,472,019; 4,572,610; 4,716,209; 5,093,386; 5,384,342; 5,456,984; 5,596,669; and copending U.S. Pat. application 08/701,428, which are hereby fully incorporated herein by reference. These patents demonstrate that urethane acrylate oligomers have become well-known in the optical fiber industry.
An objective of the present invention is to provide radiation-curable compositions that are adaptable for use as inner primary coatings, outer primary coatings, colored secondary coatings, ink coatings, bundling materials, ribbon matrix materials and colored matrix materials on optical fibers, which when suitably cured exhibit enhanced resistance to thermal degradation, are non-yellowing and/or have low coefficients of friction, with compositions directed to secondary coatings, ink coatings, bundling materials, and matrix materials being preferred.
The above objectives and other objectives are obtained by the following. It has now been found that the urethane and polyether linkages commonly used in inner primary coatings, outer primary coatings, colored outer primary coatings, ink coatings, and matrix materials are susceptible to thermal degradation if present in large amounts. The present invention provides radiation-curable compositions with low, or substantially no urethane and polyether linkages to provide optical fiber coatings and matrix materials having enhanced resistance to thermal degradation. The radiation-curable compositions according to the present invention provide coatings and matrix materials having excellent outdoor durability, resistance to discoloration, and excellent mechanical properties.
The present invention provides a novel radiation-curable, optical fiber coating composition having enhanced color stabilization when suitably cured. The radiation-curable, optical fiber coating composition is formulated from a composition including at least one radiation-curable oligomer containing a backbone formulated from monomers including acrylic acid, methacrylic acid, or a mixture thereof, and at least one radiation-curable functional group bound to the backbone, the oligomer having a number average molecular weight of from about 500 to about 200,000, wherein the urethane concentration in the composition is less than 5% by weight, based on the total weight of the composition.
The present invention also provides a novel radiation-curable composition which is formulated from a composition including at least one radiation-curable oligomer or monomer, wherein a concentration of urethane and ether linkages in the radiation-curable composition is such that a cured optical fiber coating formed from the radiation-curable composition exhibits a xcex94E of about 40 or less after being exposed to 96 hours at 150xc2x0 C. and then 144 hours at 180xc2x0 C.
The present invention further provides a novel radiation-curable optical fiber coating composition having a low coefficient of friction without the use of slip additives when suitably cured including the following combination of pre-mixture ingredients:
(A) between about 10 wt. % and about 95 wt. % of at least one radiation-curable oligomer comprising an acrylic backbone and at least one radiation-curable acrylate group, wherein the oligomer is substantially urethane-free;
(B) between about 5 wt. % to about 95 wt. % of one or more monomer diluents;
(C) optionally, an effective amount of at least one photopolymerization initiator.
The present invention provides a radiation-curable composition for fiber optic materials comprising the following combination of pre-mixture ingredients:
at least two radiation-curable compounds, wherein at least one of the compounds is a radiation-curable oligomer comprising at least one acrylate group and an acrylic oligomeric backbone, the compounds being substantially urethane-free,
optionally, at least one photoinitiator,
wherein the amounts of the pre-mixture ingredients are effective to provide the radiation-curable composition with a viscosity of about 1,000 cps to about 10,000 cps.
The present invention also provides a novel coated optical fiber comprising:
an optical fiber;
at least one coating on the optical fiber having enhanced resistance to thermal degradation. The coating has a concentration of urethane and ether linkages that provides a xcex94E of about 40 or less after being exposed for 96 hours to 150xc2x0 C. and then for 144 hours to 180xc2x0 C.
The present invention also provides a novel radiation-curable, matrix forming composition having enhanced color stabilization when suitably cured. The composition is formulated from a composition comprising at least one radiation-curable oligomer or monomer. A concentration of urethane and ether linkages in the radiation-curable composition is such that a cured matrix material formed from the radiation-curable composition exhibits a xcex94E of about 40 or less after being exposed for 96 hours to 150xc2x0 C. and then for 144 hours to 180xc2x0 C.
The present invention further provides a novel ribbon assembly comprising:
a plurality of optical fibers;
a matrix material binding the plurality of coated optical fibers together and having enhanced resistance to degradation caused by heat. The matrix material has a concentration of urethane and ether linkages that provides a xcex94E of about 40 or less after being exposed for 96 hours to 150xc2x0 C. and then for 144 hours to 180xc2x0 C.